It is desirable that the physical model eye is realistic in that it is substantially life-size having a realistic cornea, iris, lens and focal distance, and a similar field of view to a natural eye.
While such schematic model eyes are able to simulate the optical characteristics of the eye mathematically, they are not useful for assessing the performance of real corrective lenses IOLs (intraocular lenses) in combination with the eye.
Some physical model eyes of the prior art are intended to demonstrate basic eye functions to groups of students and are therefore greatly enlarged, simplified and not optically realistic. Examples are U.S. Pat. No. 1,042,815 [Myers 1912], U.S. Pat. No. 1,630,944 [Ingersoll, 1927] and U.S. Pat. No. 2,068,950 [Hamilton, 1937]. Such physical models are neither optically nor anatomically accurate and are therefore quite unsuited for the realistic evaluation of pathologies, treatments or corrective lenses.
Known physical model eyes of more relevance are those that attempt to accurately simulate selected optical and physical characteristics of the natural eye in order to test real eyewear or to calibrate ophthalmological instruments.
U.S. Pat. Nos. 5,532,770 and 5,652,640 [Schneider 1996] disclose a horizontally-mounted model eye system for evaluating IOLs, the system having a cornea, a liquid-filled posterior chamber containing the IOL, a fovea window located near the fovea and a fovea projector (a telescopic optical instrument) located behind the fovea window to allow a person to inspect the image at the fovea window. The chamber has a flexible bladder-like joint that allows the fovea projector to be moved axially relative to the IOL while retaining the liquid in the chamber. Off-axis portions of the retinal image are not of interest and no provision is made for their visualization.
U.S. Pat. No. 5,875,017 [Ohnuma et al 1997] discloses a lens system for evaluating a test IOL or contact lens that employs a CCD camera sensor located to capture the fovea image. While the test IOL or contact lens can be realistic and an accurate anterior cornea surface can be provided to support the test contact lens, the lens system is not realistic as it depends on a wide-angle camera-type objective lens placed in front of the system to bring an image to focus over the flat area of the CCD camera sensor.
U.S. Pat. No. 6,485,142 [Sheehy, 2002] discloses a horizontally-mounted, two-chamber, spherical, liquid-filled model eye that is about 6.5 times the size of a natural eye and has lenses to simulate the natural cornea and lens. It is used to evaluate protective filters and eyewear located between a radiation source and the model eye. The posterior spherical surface of the model eye, representing the retina, is translucent (frosted) and a radiation sensor (such as a CCD camera) is located outside the eye where it can detect the radiation intensity of a portion of the image formed on the frosted retina. For this purpose, the sensor can be moved concentric with the retina surface in the horizontal plane so that the radiation intensity at different angles can be examined.
U.S. Pat. No. 6,626,535 [Altmann 2003] et al discloses a single-chamber, liquid-filled and vertically-mounted model eye for testing real contact lenses. In one embodiment, the cornea and eye lens are jointly simulated by a solid optical element having an anterior surface machined to the shape of a natural cornea and having a posterior surface that forms the anterior end of the posterior chamber. A contact lens can be placed on the model cornea in a centered or decentered manner, as desired. The retina is simulated by a transparent or reflective concave surface that forms the posterior end of the chamber. A flexible bladder-like joint allows the retina surface to be moved to change eye-length or to vary centration of the retina surface while retaining the liquid in the chamber. Whilst the use of a pinhole-like fovea window is disclosed, evaluation of the test contact lens is performed by refractometer or wavefront instruments located in front of the eye that rely upon reflection from the model retinal surface. However, the incident angles at which such instruments can be used effectively, are severely limited.
U.S. Pat. No. 7,036,933 [Yamaguchi, 2006] discloses a horizontally-mounted tubular model eye for use in calibrating wavefront measuring instruments used on natural eyes. It is not physically realistic in shape or in the contours of the optical surfaces. An anterior lens simulates both the natural cornea and lens and a posterior diffusion surface is located at the focal point of the lens to simulate the fundus of the retina. A phase plate is inserted between the lens and the diffusion surface to correct for aberrations introduced by the lens or to add controlled aberration to the model eye. An interferrometric calibration method using the model eye is also disclosed.
U.S. Pat. No. 7,066,598 [Niven 2006] discloses a vertically-mounted two-chamber model eye capable of accommodating separate liquids representing both humors. The model cornea appears to have a realistic posterior surface as well as a realistic anterior surface, the natural lens is represented by a solid machined lens, the iris is simulated by an aperture ring located in front of the lens and is used to mount the lens within the posterior chamber, and the retina is simulated by the flat inner surface of an end cap that seals the posterior chamber of the model eye and is located at a fixed distance from the lens. A feature of this model is the provision of gaps between the iris ring and the lens to permit air trapped in the posterior chamber to gravitate upward into the anterior chamber. The model eye is used with refractometers or the like in the same manner as that of Altmann and also can be used for refractometer calibration.
It will be understood that any reference herein to prior art does not constitute an admission as to the common general knowledge of a person skilled in the art.